ESEEM studies of penta-coordinate deoxyCo porphyrin models and deoxyCo myoglobin have demonstrated that the ESEEM spectra arise from electron-nuclear coupling to the equatorial porphyrin nitrogens and to the remote nitrogen of the axial imidazole. Preliminary ESEEM studies of the deoxyCo-substituted subunits of unligated and diligated iron-cobalt hybrid hemoglobins have shown that the relative intensities of the quadrupole lines of the axial remote nitrogen (the Nn of the proximal histidine) vary with the type of the subunit and in the case of the deoxyCo ` subunits with the ligation state of tetramer as well. ESEEM spectra of deoxyCo porphyrin models and deoxyCo myoglobin are being analyzed, with primary focus on obtaining tensor orientations by spectral simulation. The tensor orientations ar then correlated with molecular structures using the g tensor assignment of deoxyCo myoglobin, and the nuclear quadrupole tensor assignments for the remote nitrogen of imidazole ligands of copper. the orientation of the axial imidazole plan with respect to the normal of the porphyrin plane and with respect to a N(pyrrole)-Co-N-(pyrrole) axis in deoxyCo (tetraphenylporphyrin) (1,2-dimethylimidazole), deoxyCo (TPP) (1-methylimidazole) and deoxyCo myoglobin, obtained by simulation of ESEEM spectrum, is within 10x of that revealed by X-ray crystal structures.